Copy Protection System for Data Carriers

ABSTRACT

A copy-protected compact disc includes, within a single session, a table of contents (TOC) and a Video CD index (VI). Each track (T) is prefaced by unrecoverable data (UD) at a track start position (ATOC) indicated by the table of contents (TOC). However, the Video CD index (VI) indicates the actual position (AP) of the tracks. DVD players use the Video CD index (VI) to locate the tracks, while the CD-ROM drives use the table of contents (TOC) and read the unrecoverable data (UD), which prevents them from reading the subsequent track (T). The unrecoverable data (UD) may be prefaced by data pointers (DP) which cause the CD-ROM drive to load a player program in response to the error condition. The player program can be used to play the tracks (T), but restricts copying. Subchannel data (P; DX) causes audio CD players to ignore the Video CD index (VI) and the unrecoverable data (UD), and to play the tracks (T) at their actual start positions (AP).

FIELD OF THE INVENTION

This invention concerns methods, software and formats for preventing orrestricting copying of data, particularly as recorded in digital form ona carrier such as optical disc media. In this description optical discmedia is intended to include compact discs (CDs), CD-ROMs and DigitalVersatile Discs (DVDs), as well as similar media that may be read usingelectromagnetic radiation outside the visible range.

BACKGROUND OF THE INVENTION

CD audio discs contain at least a first session formatted in compliancewith the well known ‘Red Book’, also known as Standard 908 of theInternational Electrotechnical Commission (IEC) entitled ‘Compact DiscDigital Audio System’ (Geneva, Switzerland, 1987).

CD-ROMs contain one or more sessions formatted in compliance with the‘Yellow Book’ standard and normally its extension ‘System DescriptionCD-ROM XA’, which includes a data retrieval structure based on ISO 9660.The ‘Yellow Book’ standard incorporates the ‘Red Book’ standard, so thatCD data drives can play audio data as well as read non-audio data.Multisession CD-R and CD-RW discs comply with the Orange Book standard.

In this specification, a distinction will be made between ‘audio CDplayers’, which need only be able to read CDs complying with the RedBook standard, and ‘CD-ROM drives’, which are able to read CD'scomplying with the Yellow Book standards, and normally the Orange Bookstandard as well. Audio CD players are generally stand-alone deviceshaving no other functionality than audio reproduction, although they maybe integrated with other devices. CD-ROM drives are peripherals forgeneral-purpose computers or other similar devices which are able toload and run application programs selected by the user.

The advent of recordable CDs (CD-R) has made it generally easy andinexpensive to make unauthorised copies of audio CDs and CD-ROMs; forexample by copying the entire contents of an audio CD to a computer harddisc and then writing this to a CD-R. The potential loss of revenue torecording companies from such activities is considerable, and indeed itsimpact has already been felt. Consequently, there is a need to preventsuch unauthorised copying.

Red Book compliant CDs contain a great deal of information which is notnecessary purely for playing audio tracks and which is ignored by mostaudio-only players. Hence, one approach to preventing unauthorisedcopying has been to deviate from Red Book compliance in a way that isignored by audio CD players, but causes an error in a CD-ROM drive.

Examples of this approach are described in WO 00/74053, in whichselected control data is rendered inaccurate or incorrect; the Table ofContents (TOC) may identify the audio tracks as data tracks, or mayincorrectly identify the position of the Lead-Out. WO 02/075735discloses identifying the first session as CD-ROM data when it actuallycontains audio tracks. EP 1239472 also discloses the idea of identifyingaudio tracks as data tracks in the TOC.

The techniques mentioned above are intended to prevent reading of audiotracks by a CD-ROM drive, and thereby prevent storage of the tracks on acomputer and subsequent recording or distribution on some other medium.However, some users would like to play audio CDs on their computers.Hence, there is also a need to provide audio tracks in such a way thatthey can be played on a CD-ROM drive but cannot be re-recorded ordistributed.

One solution to this problem has been to provide the audio tracks in afirst session which cannot be read by a CD-ROM drive, and to provide anencrypted version of the audio tracks in a second session. The encryptedtracks can only be decrypted and played by a player program which playsthe audio data by converting it to audio signals.

However, certain multifunction devices such as DVD players also conformto the Yellow Book standard and are therefore prevented from reading theaudio tracks. Furthermore, multifunction devices may not be capable ofloading and running a player program to decrypt and read a secondsession. Hence, a multifunction device such as a DVD player may not beable to reproduce any of the content of a copy-protected CD, despitebeing incapable of producing unauthorised copies. This problem is notunique to DVD players. For example, MP3-enabled CD players, automotiveaudio systems where the CD player is used to read mapping informationfor a navigation system as well as to play audio CDs, and games consolesmay all be sensitive to modified control data in the first session, butincapable of running a player program to decrypt a second session. Thesensitivity to modified control data in the first session depends onwhether a suitable recovery strategy is programmed into the firmware ofthe device. Multifunction devices which are not general-purposecomputers are normally not reprogrammable, but contain all of thenecessary programs in firmware, and cannot therefore load a new playerprogram for playing the second session.

Another problem is that the second session occupies a significantproportion of the CD, and yet typically contains duplicate content tothe first session. Hence, the use of a second session restricts thequantity of content which can be recorded on a single CD.

STATEMENT OF THE INVENTION

According to one aspect of the present invention, a compact discincludes, within a single session, different indexes each recognisableby a different class of compact disc player. One index gives the startaddresses of the payloads of tracks, and allows the class of playerwhich reads that index to play the tracks. That class may be Video CDcompatible players. A second index gives addresses for encapsulatingdata which prefaces some or all the tracks, leading a second class ofplayer to read the encapsulating data instead of the tracks. Theencapsulating data causes the second class of player to start a playerprogram which allows playback but not copying of the tracks. The secondclass may be CD-ROM drives. The encapsulating data and the other indexare recorded in such a way that a third class of player ignores them,and plays the tracks. The third class may be audio CD players.

Thus, a single session may contain tracks which are readable by each ofthe three different classes of CD player, but restricts copying of thetracks by the second class of player, which is otherwise able to copythe tracks.

According to another aspect of the present invention, there is provideda method of preventing access to a removable storage medium, such as aCD or DVD, by unauthorised applications, comprising interceptingcommands sent through an application program interface to the drive,preventing normal operation of standard commands, and enabling operationof non-standard commands by converting non-standard commands to standardcommands and sending them to the drive. Unauthorised programs do notnormally generate non-standard commands, and are therefore preventedfrom controlling the drive, while authorised programs use non-standardcommands to control the drive. This aspect of the invention provides aconvenient way of distinguishing between authorised and unauthorisedprograms.

The present invention extends to a method of recording the compact disc,a computer program for performing the method, and the data structure ofthe compact disc.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the preferred embodiments will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of a session format in an embodiment of theinvention;

FIG. 2 a is a diagram of a driver chain between an application and aCD-ROM drive;

FIG. 2 b is a diagram showing the insertion of a supervisory program inthe driver chain;

FIG. 3 a is a diagram showing the action of a command proxy function inthe supervisory program when receiving a command proxy from a higherlayer;

FIG. 3 b is a diagram showing the action of a command proxy function inthe supervisory program when receiving a standard command from thehigher layer, and

FIG. 4 is diagram illustrating the stages of manufacture of a compactdisc according to the embodiment.

DESCRIPTION OF THE EMBODIMENTS Multiple File Systems in Single Session

In an embodiment of the invention, a compact disc (CD) carries a singlesession incorporating multiple data structures each complying with afiling system of a different standard. hi this embodiment, the singlesession includes multiple different data structures readable byPC-compatible computers, Mac™ computers, Red Book standard audio CDplayers, and White Book standard video CD players. The track format iscompatible with the relevant standard for that track type. In this way,a player can recognise one of the data structures in order to access thetracks, and can play the tracks if it is able to decode their format.However, the data structures readable by PC-compatible and Mac™computers include unrecoverable data, which prevent the computer fromreading the tracks unless by means of a dedicated player program whichprevents unauthorised copying of the tracks.

FIG. 1 shows a sample format of a single session in an embodiment of theinvention. The single session contains a lead-in LI, a program area PAcontaining one or more tracks T1-TN, and a lead-out LO. The lead-in LIincludes a table of contents (TOC), identifying the absolute times(ATIME) of the start of each track and of the lead-out LO.

The tracks T1-TN conform to the Red, Yellow and White Book standards asappropriate to each track. These formats are well known, but therelevant parts are recited here for ease of understanding. Each frame ofdata which is modulated and recorded on the CD includes one subcodebyte. Each bit of the subcode byte corresponds to a different subcodechannel, labelled from P to W. The P-channel is a single bit that goeshigh during an optional pause between tracks and goes low during thetrack. The Q-channel contains time codes, track type and catalogueinformation and, in the Lead-in, the TOC. The time codes include ATIME,the absolute time elapsed since the start of the session in the formatM:S:F denoting minutes, seconds and frames. The Q channel also indicatesthe track number TNO, which increments during the pause preceding atrack, and the index IDX which changes from ‘00’ indicating a pause to‘01’ indicating a track.

As shown in FIG. 1, there is an extended pre-gap area PG containingmultiple different data structures preceding the first track T1. Thefirst data structure is a Mac™ boot sector MB containing a pointer to anHFS sector HS containing a Mac™ compatible player application, asdescribed below. Thus, a Mac™ class computer, on mounting the CD, willload and run the Mac™ compatible player application.

Next, there are recorded data pointers DP required by the ISO 9660standard: the Primary Volume Descriptor (PVD), Supplementary VolumeDescriptor (SVD), and Volume Set Descriptor (VSD). The data pointers DPpoint to ISO 9660/Joliet files JF, containing a PC-compatible playerapplication, as described below, and to duplicate data pointers DPpreceding unrecoverable data UD as will be described below under theheading ‘Data Encapsulation’.

Next, there is recorded a Video CD index section VI containing the files‘info.vcd’ and ‘entries.vcd’, recorded at ATIME of respectively 00:04:00and 00:04:01. According to the White Book standard, this section VIwould normally be included in a segment play area of the disc, but inthis embodiment, it is included in the extended pre-gap area PG. As aresult, the index section VI is ignored by CD audio players and is notvisible in the ISO 9660 Joliet or HFS filing systems.

Most DVD players identify a VCD type disc by looking for the files‘info.vcd’ and ‘entries.vcd’ at ATIME of respectively 00:04:00 and00:04:01, and will therefore find these files at the expected positionand disregard the ISO 9660 data structure. The VCD index section VI isnot indexed in the HFS or Joliet filing systems, and will therefore notbe found by PC-compatible and Mac™ class computers.

The file ‘entries.vcd’ comprises an index of the positions of tracksreadable under the VCD format in the disc. The index includes the actualstart positions AP of each of the tracks T1-TN, but may also include thepositions of video segments VS stored within the pre-gap area PG. Hence,a DVD player is able to locate and play the tracks T1-TN, and any videosegments VS. According to the White Book, audio tracks conforming to theRed Book standard can be played.

Data Encapsulation

Since the tracks T1-TN are recorded in standard formats, it is desirableto prevent unrestricted access to the tracks by PC-compatible and Mac™class computers. This is achieved by a format which will be referred toas ‘data encapsulation’. In outline, data encapsulation involvesprefacing a track with unrecoverable data and a pointer to a playerprogram which is able to ignore the unrecoverable data, but whichrestricts copying of the tracks T1-TN. The unrecoverable data andpointer are recorded in a format which is ignored by players which donot conform to the Yellow Book standard, such as audio CD players. Dataencapsulation can be applied to some or all tracks in a session.

In this embodiment, data encapsulation is achieved as follows.Immediately preceding the first track T1, there is recordedencapsulating data ED. The absolute time position ATOC of first trackT1, as indicated in the TOC, indicates the first sector of theencapsulating data ED. Therefore, Yellow Book standard drives willinterpret the first Track T1 as beginning at ATOC, and will start toread the track from that point. The encapsulating data ED comprises, insequence: blank data BD; the duplicate data pointers DP; unrecoverabledata UD, and audio silence AS.

The unrecoverable data UD may be unrecoverable due to one or more ofsync information, error detection code (EDC) or error correction code(ECC) being corrupted. Alternatively, an inconsistent value of ATIME maybe written in each sector header, while the EDC and the ECC do notindicate any error in this value.

The encapsulating data ED is followed sequentially at an absolute timeposition AP by the first track T1, which conforms entirely with theappropriate standard for the relevant track type.

The P channel bit stays high at the position ATOC, but goes low at theposition AP. At this point, the index IDX changes from 00 (indicating apause) to 01 (indicating a track). Throughout the pre-gap area PG, thetrack number TNO indicates the track number of the following track (inthis case, it has the value 1). As shown in FIG. 1, each of thesubsequent tracks may be prefaced by the encapsulating data ED.

When an encapsulated track is played by a CD-ROM drive, the drive readsthe position ATOC from the TOC and starts reading at that position.First, the duplicate data pointers DP are read; the duplicate datapointers DP are included here because some CD-ROM drives may not be ableto recognise the pointers in the pre-gap area PG. When the unrecoverabledata UD is read, the data reading operation is aborted. The CD-ROM drivewill then implement a recovery strategy, which includes reading from theposition indicated by the data pointers DP. Hence, the player program isloaded automatically.

When the track is played by an audio CD player, the player starts tolook for the track T at the position ATOC but also examines othercontrol data, such as the P channel and the index IDX, to determine thestart position of the track T. The player therefore starts to read thetrack from the time AP, thereby avoiding the encapsulating data ED andplaying the track as a normal audio track.

By this method, a CD-ROM drive encounters an error in the data itself,rather than in the control information. The method cannot becircumvented simply by ignoring all data errors, because there may beunintentional data errors elsewhere on the CD which cannot be ignored.

A multifunction device which detects video CDs by looking for the files‘info.vcd’ and ‘entries.vcd’ at a predetermined position on the compactdisc will use the track index contained within those files; as the trackindex indicates the start position as AP, rather than ATOC, theencapsulating data ED is not read by the multifunction device.

Player Program

As described above, the CD contains both a Mac™ player program and aPC-compatible player program, each arranged so that it is onlyidentified by the relevant filing system. The player program is designedto read the CD in the same manner as a DVD player, by reading the VCDindex section VI at the predetermined position as described above. Theplayer program does not attempt to read the encapsulating data ED.However, the player program is arranged to play the tracks only if asupervisory program, as described below, is running on the computer.

Supervisory Program

Preferably, a disc produced according to the embodiment containssoftware that is activated when the computer operating system firstaccesses the disc; this may be done automatically using an ‘autorun’function of the operating system. The software may comprise visible,hidden, or a combination of visible and hidden files on the disc. Thesoftware may comprise multiple files, packaged into a single packagefile.

The software may conceal critical registry entries by deploying filterswithin the host operating system. This makes it difficult to inhibit thesoftware by changing registry entries.

The software instantiates a memory resident supervisory program thatmonitors access to the protected disc. When the disc is removed, thesupervisory program is removed from the memory of the PC. Thesupervisory program is also designed to monitor the activity of thedisc, including disc speed and disc access type (digital or audio) andto ensure reliable playback of the disc content.

The supervisory program inserts itself or part of itself into theoperating system driver chain. As illustrated in FIG. 2 b, a driverchain is a computer operating system feature, where an application APPcommunicates with a higher level HL of the chain. This higher level HLcommunicates with a lower level LL which communicates with the CD-ROMdrive. The driver chain presents a standard application programinterface API to the application program APP for communicating with alarge variety of hardware devices. As shown in FIG. 2 b, the supervisoryprogram SP inserts itself into this driver chain by modifying the chainpointers in the next highest and lowest levels, and can thereforemonitor all communications from the application program APP to theCD-ROM drive. The supervisory program SP performs command monitoring anddisc monitoring functions.

Command Monitoring

The command monitoring function intercepts commands, such as SCSI orATAPI commands, sent by the application APP to the CD-ROM drive anddetermines whether the commands indicate an unauthorised activity, suchas the reading of data from the disc by an application that is not theplayer program. If an unauthorised activity is detected, the relevantcommand is blocked by the supervisory program and cannot continue downthe driver chain to the CD-ROM. A command response is generated by thesupervisory program and is returned up the driver chain to theapplication. The response may be an error message or dummy data, whichappear to have originated from the CD-ROM drive, and prevent theapplication from performing the desired operation.

Alternatively, the command monitoring function may pass a read commandto the disc, but may corrupt the data read from the disc if the readoperation is not authorised, so that the application receives corruptdata.

Command Proxy

The command monitoring function is able to handle non-standard commands,referred to as ‘Command Proxies’, sent by the application to the drive.Command proxies are not recognisable by the drive and are only used byauthorised applications. The codes for command proxies may be keptsecret, so that unauthorised applications cannot be programmed to usethem.

As shown in FIG. 3 a, when the command monitoring function of thesupervisory program SP receives a command proxy CP, it alters thecommand proxy to a standard drive command and passes the standardcommand C on to the drive. The drive processes this command as normaland returns the result D to the supervisory program SP, which generatesa corresponding result D to send to the application program APP. Forexample, a ‘read’ command proxy CP causes the command monitoring programto send a standard read command C to the drive. The drive returns theread data D which is passed on to the application program.

Conversely, as shown in FIG. 3 b, the command monitoring function of thesupervisory program SP blocks standard commands, which are recognisableby the drive, received from an application program. For example, whenthe normal read command C is used, its operation is blocked by thecommand monitoring program, and an error message E may be returned.

In a more specific example, the commands C are standard SCSI commandssuch as defined in draft standard ANSI T10 MMC and the SCSI PrimaryCommands standards SCP-2 and SCP-3. Both SCSI and ATAPI drives use thestandard SCSI command set. The command proxies CP conform with the SCSIcommand standard, except that their command codes do not have anystandard meaning and are therefore not recognisable by drives conformingto the SCP standards. However, the command monitoring function accessesa conversion table that converts command proxies CP to standard commandsC, and is therefore able to recognise command proxies CP and sendequivalent standard commands to the drive.

Disc Monitoring

The disc monitoring functions involve monitoring data read by the CD-ROMand passed along the driver chain to the application. If unauthorisedactivity is detected, the read operation is prevented.

The supervisory program SP may, for example calculate the average datatransfer rate, disc speed or the type of read operation that is beingattempted. When a disc is being played in a computer using the playerprogram, the average data reading speed of the disc will beapproximately the same as the speed at which the player program playsthe data. The data may read from the disc in blocks at a high speed(burst speed), followed by a much longer period of inactivity. The burstspeed could in fact be anything up to and including the maximum readspeed of the CD-ROM drive, but for very short periods. On the otherhand, CD copying software typically will try to copy at the highestspeed possible for a sustained period. The supervisory program monitorsthe average data reading speed over a predetermined period, such as tenseconds. If the average speed exceeds a threshold, then the readoperation is prevented.

The supervisory program may monitor the position of the read head of theCD-ROM and compare the position to a range of positions that the playerprogram should not need to access. If a position within that range ofpositions is being accessed, the supervisory program prevents the readoperation. For example, the player program should not attempt to readthe encapsulating data, so the range of positions may include thepositions of the encapsulating data ED. If the supervisory programdetects that the player program is running but the encapsulating data isbeing read, then the reading operation is inhibited. The read operationmay be prevented by blocking the data from reaching the application, andreturning an error message, dummy data or corrupt data as describedabove. The supervisory program may shut down the unauthorisedapplication. An eject command may also be sent to the CD-ROM.

The supervisory program interacts with the player program to preventunauthorised activities. If the player program is not open, or is closedby the user while the disc is still in the CD-ROM drive, then thesupervisory program sends an eject command to the CD-ROM drive.Likewise, if a protected disc is no longer present in the CD-ROM drive,the supervisory program closes itself down.

The supervisory program may comprise multiple program components, eachof which checks for the presence of some or all of the other componentsand restores any of the other components which have been removed orcorrupted. This makes it very difficult for the supervisory program tobe removed in an unauthorised manner.

Where there is more than one protected disc accessible to the computerat the same time in different drives, the supervisory program, whenlaunched by the insertion of a protected disc, determines whether thereis another instance of itself already running. If so, the drivecontaining the new disc is added to a list of drives monitored by theother instance. If not, the new instance of the supervisory program isdeployed. Once all of the monitored drives no longer contain a protecteddisc, the supervisory program removes itself from the system.

In general, the supervisory program is designed to detect any access toa protected disc other than the player program accessing the disc. Ifthe disc is accessed in any other way the activity will be judgedillegal and interventionary action will be taken by the supervisoryprogram. The supervisory program identifies a protected disc byrecognising a signature which forms part of the disc format structure,and does not prevent the copying of an ordinary disc or interfere withthe general performance and/or activities of the computer.

CD Production

To produce a CD formatted according to an embodiment of the inventionrequires special software to be used during the mastering process, whichis illustrated in FIG. 4. The source data D for one or more tracks isprovided on a carrier, which may itself be a recordable CD or a digitaltape. The source data is formatted (S10) by software to generate asession and associated data in the format described above, for recordingon the CD. The formatted data is recorded (S20) on a CD master, usingfor example a laser beam recorder which writes the data on a coatedglass master. The glass master is developed (S30) to produce ametallized glass master M. The master may be used to produce one or morestampers S by an electroforming process (S40). CDs are mass-producedfrom the stamper S by a stamping process (S50). In an alternativeembodiment suitable for low volume production, recordable CD's may berecorded directly with the formatted data.

The formatted data may be recorded as a data set for input to therecorder at a subsequent time.

Embodiments of the invention include CD production software forformatting data and/or controlling a recording process to generate oneor more CD's having a format in accordance with an embodiment of theinvention. Embodiments also include formatted data having a structure asdefined above.

The above embodiments are provided purely by way of example.Alternatives, which may be apparent to the skilled person on reading thespecification, may nevertheless fall within the invention as defined bythe claims.

1-50. (canceled)
 51. An optical disc carrying a session including atable of contents and a program area containing at least one track, thetable of contents indicating a first start position, wherein: a. a dataportion is located at said first start position and is arranged to causea read failure by a first optical disc reader, which reads at said firststart position; b. the track is located at a second start positiondifferent from said first start position; and c. the session furtherincludes an index indicating said second start position, such that asecond optical disc reader is enabled to read the track by reading thesecond start position from the index.
 52. An optical disc according toclaim 51, wherein the index is a video CD index and said second opticaldisc reader is a video CD compatible optical disc reader.
 53. An opticaldisc according to claim 51, wherein the index is located at apredetermined position within the session, such that it is recognised bythe second optical disc reader.
 54. An optical disc according to claim51, wherein the program area includes one or more subchannels arrangedto cause a third optical disc reader to read the track and to ignore thedata portion.
 55. An optical disc according to claim 54, wherein the oneor more sub channels are arranged to cause the third optical disc readerto ignore the index.
 56. An optical disc according to claim 54, whereinthe third optical disc reader is an audio CD player, and the track is anaudio track.
 57. An optical disc according to claim 51, wherein the dataportion includes unrecoverable data arranged to cause a read error inthe first optical disc reader.
 58. An optical disc according to claim51, wherein the data portion includes a pointer to a player programexecutable by the first optical disc reader to play the track.
 59. Anoptical disc according to claim 58, wherein the pointer indicates aposition on the optical disc at which the player program is stored. 60.An optical disc according to claim 58, wherein the data portion isarranged to cause the first optical disc reader to execute the playerprogram.
 61. An optical disc according to claim 58, wherein the playerprogram is arranged to restrict copying of the track by the firstoptical disc reader.
 62. An optical disc according to claim 51,including a boot sector arranged to cause a third optical disc player toexecute a player program when the optical disc is loaded into the thirdoptical disc player.
 63. An optical disc according to claim 62, whereinthe player program is arranged to restrict copying of the track by thethird optical disc player.
 64. An optical disc according to claim 62,wherein the player program is stored on the optical disc at a positionindicated by the boot sector.
 65. An optical disc according to claim 51,further including a supervisory program arranged to be executed by thefirst optical disc player when the optical disc is loaded therein, thesupervisory program being arranged selectively to prevent access to theoptical disc by the first optical disc player.
 66. An optical discaccording to claim 51, wherein the track is able to be copied to anothercarrier via the first optical disc reader.
 67. An optical disc accordingto claim 51, wherein the track is unable to be copied by the secondoptical disc reader to another carrier.
 68. An optical disc according toclaim 51, wherein the program is unable to be loaded and executed by thesecond optical disc reader.
 69. A method of manufacturing an opticaldisc, the method comprising: formatting source data to create a sessionincluding a table of contents and a program area containing at least onetrack, the table of contents indicating a track start position; andrecording the formatted source data on the optical disc, wherein: a. adata portion is located at said first start position and is arranged tocause a read failure by a first optical disc reader, which reads at saidfirst start position; b. the track is located at a second start positiondifferent from said first start position; and c. the session furtherincludes an index indicating said second start position, such that asecond optical disc reader is enabled to read the track by reading thesecond start position from the index.
 70. A method according to claim69, wherein the index is a video CD index and said second optical discreader is a video CD compatible optical disc player.